BIRSTALL, England A British member of Parliament was shot dead in the street in northern England on Thursday, causing deep shock across Britain and the suspension of campaigning for next week's referendum on the country's EU membership.

Jo Cox, 41, a lawmaker for the opposition Labour Party and vocal supporter of Britain remaining in the European Union, was attacked as she prepared to hold a meeting with constituents in Birstall near Leeds.

Media reports said she had been shot and stabbed.

West Yorkshire Police said a 52-year-old man was arrested by officers nearby and weapons including a firearm recovered. The motive for the attack was not immediately known.

"The whole of the Labour Party and Labour family - and indeed the whole country - will be in shock at the horrific murder of Jo Cox today," Labour leader Jeremy Corbyn said in a statement.

Prime Minister David Cameron said the killing of Cox, who was married with two children and had worked on U.S. President Barack Obama's 2008 election campaign, was a tragedy.

"We have lost a great star," the Conservative prime minister said in a statement. "She was a great campaigning MP with huge compassion, with a big heart. It is dreadful, dreadful news."

British lawmakers are not in parliament ahead of the June 23 referendum on whether Britain should remain in the EU.

The rival referendum campaign groups said they were suspending activities for the day and Cameron said he would pull out of a planned rally in Gibraltar, the British territory on the southern coast of Spain.

It was not immediately clear what the impact would be on the referendum.

"It's fairly clear no one is quite sure what has happened," said John Curtice, professor of politics at the University of Strathclyde. "Until it's clear who was responsible and what their motivation was or it might have been, all it does is stop the campaign when the 'Remain' side probably would not want it to be stopped."

The pro-EU "Remain" campaign has fallen behind the "Leave" camp in pre-referendum polls.

The last British lawmaker to have been killed in an attack was Ian Gow, who died after a bomb planted by the Irish Republican Army (IRA) exploded under his car at his home in southern England in 1990.

MAKESHIFT GUN PULLED FROM BAG

Police said a 77-year-old man was also assaulted in the incident and suffered injuries that were not life-threatening.

One witness said a man had pulled an old or makeshift gun from a bag and had fired twice.

"I saw a lady on the floor like on the beach with her arms straight and her knees up and blood all over the face," Hichem Ben-Abdallah told reporters. "She wasn't making any noise, but clearly she was in agony."

BBC TV and other media showed a picture of the alleged suspect, a balding white man, being apprehended by police.

Dee Collins, the Temporary Chief Constable of West Yorkshire Police, said a full investigation was under way into the motive for the attack.

"This is a very significant investigation with large numbers of witnesses who have been spoken to by police at this time," she told reporters. "We are not in a position to discuss any motive at this time. We are not looking for anyone else in connection with this incident."

Media reports citing witnesses said the attacker had shouted out "Britain First", which is the name of a right-wing group that describes itself on its website as "a patriotic political party and street defence organisation".

Jayda Fransen, deputy leader of Britain First, said the attack was "absolutely disgusting" and suggested that Britain first was a common slogan being used in the referendum campaign by those who support taking Britain out of the EU.

"We were as shocked to hear these reports as everyone else," Fransen told Reuters. "At the moment would point out this is hearsay, we are keen to verify the comments but we can only do that when the police provide more details."

Britain's sterling currency rose against the dollar after news of the attack, adding around two cents as investors speculated that Cox's death might boost popular support for the referendum "Remain" campaign.

The last attack on a British legislator was in 2010, when Labour member and ex-cabinet minister Stephen Timms was stabbed in the stomach at his office in east London by a 21-year-old student who was angry over his backing for the 2003 Iraq war.

In 2000, a Liberal Democrat local councillor was murdered by a man with a samurai sword at the offices in western England of lawmaker Nigel Jones, who was also seriously hurt in the attack.

Cox, a Cambridge University graduate, spent a decade working in a variety of roles with aid agency Oxfam, including head of policy, head of humanitarian campaigning based in New York and head of its European office in Brussels.

She was known for her work on women's issues, and won election for Labour in northern England's Batley and Spen district at the 2015 general election.

Fellow lawmakers from several parties expressed their horror at the attack, praising Cox as a rising star of politics.

"She's a tiny woman, five feet nothing and a lion as well - she fights so hard for the things she believes in. I cannot believe anyone would do this to her," fellow Labour lawmaker Sarah Champion told BBC TV.